NASA’s Dawn spacecraft unlocks secrets of giant asteroid
Image showing the south pole of the giant asteroid Vesta obtained by the framing camera on NASA's Dawn spacecraft
After becoming the first probe to enter orbit around an object in the main asteroid belt between Mars and Jupiter in July 2011, NASA’s Dawn spacecraft
has spent the last 10 months orbiting said object - the giant asteroid
Vesta. During that period it has captured more than 20,000 images of
Vesta and a multitude of data from different wavelengths of radiation.
What it reveals is an asteroid that in many ways shares more in common
with a small planet or Earth’s moon than it does with another asteroid.
With a mean diameter of around 326 miles (525 km), Vesta is one of
the largest asteroids in the Solar System and the second most massive
after Ceres. Formed in a similar way to the terrestrial planets and
Earth’s moon, Vesta boasts a geologic complexity that scientists
attribute to a process that separated it into a crust, mantle and iron
core with a radius of around 68 miles (110 km) some 4.56 billion years
ago.
"Vesta has been recording the history of the solar system from the
beginning," said Christopher T. Russell, a professor in UCLA's
Department of Earth and Space Sciences and the Dawn mission's principal
investigator. "We are going back to the beginning of the solar system -
more than 4.5 billion years ago. We're going back further than ever
before on the surface of a body."
Deep gashes in Vesta’s surface observed by Dawn reveal a pattern of
minerals that NASA says may suggest the asteroid was once molten inside
and had a subsurface magma ocean, which occurs when a body undergoes
almost complete melting and leads to layered building blocks that can
form planets. Vesta’s iron core would have formed during this molten
period at the dawn of the Solar System.
Data collected by Dawn also reveal that Vesta is the source of a
distinct group of meteorites found on Earth. These meteorites, with
signatures of an iron- and magnesium-rich mineral known as pyroxene,
account for about six percent of all meteorites falling to Earth, making
Vesta one of the largest single sources of Earth’s meteorites. Dawn’s
mission also marks the first time a spacecraft has visited the source of
samples after they were identified on Earth.
Vesta has also been found to have a topography that is quite steep
and varied, and includes large mountains formed by a major impact on the
asteroid’s surface – the largest of which is more than twice the size
of Mount Everest. While scientists had thought that, outside the south
polar region, Vesta’s surface may be flat like the moon, some of the
craters outside this region formed on very steep slopes and have nearly
identical sides, with landslides often occurring.
NASA scientists were also surprised to discover that Vesta’s central
peak in the Rheasilvia basin in the southern hemisphere is much higher
and wider, relative to its crater size, than the central peaks of
craters on bodies like our moon.
There are also similarities with other low-gravity worlds, such as
Saturn’s small icy moons, and the light and dark markings on its surface
don’t match the predictable patterns seen on Earth’s moon. While
Vesta’s surface contains bright spots of various sizes, there are also
some areas that are dark as coal, with the light and dark markings
forming intricate patterns that suggest the dominance of impact
processes in creating mixed layers in Vesta’s regolith.
"We know a lot about the moon and we're only coming up to speed now
on Vesta," said Vishnu Reddy, a framing camera team member at the Max
Planck Institute for Solar System Research in Germany and the University
of North Dakota in Grand Forks. "Comparing the two gives us two
storylines for how these fraternal twins evolved in the early solar
system."
Dawn will continue to examine Vesta until it departs the asteroid on
August 26 headed for a 2015 study date with Ceres, the Solar System’s
largest asteroid and only dwarf planet in the inner solar system.
Six papers on Vesta were published in the journal Science on May 11, 2012, and more information about the Dawn mission can be had at the NASA's Dawn mission homepage.
